Fiber cement materials are being used more frequently in outdoor applications in new construction. These fiber cement materials, often in the form of flat boards, are ideal for use as roof, wall and floor sheathing and wall siding. The boards may be fiber reinforced and silicone impregnated to provide uniform structural characteristics, while being resistant to fire, rot, water damage, insects and freezing.
Because of their heavy and stiff construction, fiber cement boards have the disadvantage of being more difficult to work with than conventional wood materials. In particular, the fiber cement boards are difficult to cut with conventional tools. While hand-held circular power saws are most often used to cut the boards, conventional saw blades and other types of blades have proven less than ideal for the task.
When used on fiber cement materials, conventional blades often produce a very rough, chipped cut edge. Furthermore, the stiff nature of the fiber cement boards provides significant resistance to the teeth of a conventional circular blade, thereby straining the motor of the power tool and producing a significant amount of frictional heat at the blade edge. This excess heat can dull the blade edge rapidly and compromise the construction of the braze joint between the blade and tooth tip portions.
These conventional blades also produce a tremendous amount of dust and flying debris when cutting fiber cement board, since they typically have a large number of teeth. The dust results in a difficult working environment for the user and the silica contained in the dust is a known health hazard. Furthermore, the dust reduces visibility for the user, which can have a significant effect on the accuracy of the cuts and prove dangerous to the user.
There is therefore a need for an improved saw blade design for use with fiber cement materials that alleviates the foregoing disadvantages.
In accordance with one aspect of the present invention and in one embodiment thereof, a rotary saw blade is provided having a main body plate and a central opening with respect to an axis of rotation. A plurality of cutting teeth are disposed about the periphery of the plate. Arcuate tooth support portions extend rearwardly from the cutting teeth and have a center of curvature offset from the axis of rotation. Peaked shoulders having a forwardly sloping portion, a peak and a rearwardly sloping portion extend from the tooth support portions. The peaked shoulders partially define hook-shaped gullets between the shoulders and the cutting teeth.
In another aspect of the present invention, another embodiment of the invention may be provided in the form of a rotary saw blade for use in cutting fiber cement board material. The blade includes a generally circular main body plate having a central opening with respect to its axis of rotation. Cutting teeth are disposed about the periphery of the plate, and each tooth is preceded by a peaked shoulder. Each shoulder is at least partially defined by a forwardly sloping portion, a peak and a rearwardly sloping portion, wherein the rearwardly sloping portion has a length at least twice the length of the forwardly sloping portion. A hook-shaped gullet is defined at the periphery of the plate between each shoulder and the proximate cutting tooth. Each of the gullets is at least partially defined by the rearwardly sloping portion of an adjacent shoulder and an arcuate portion having a partially circular shape. A plurality of tooth support portions extends between the rear of each tooth to the forwardly sloping portion of the shoulder.
The invention may also be embodied in a method of cutting fiber cement board material. The method includes the steps of providing a handheld power tool and attaching a blade to the power tool. The blade includes a main body plate having a central opening with respect to an axis of rotation and between four and ten cutting teeth disposed about the periphery of the plate. A plurality of arcuate tooth support portions extend rearwardly from the cutting teeth and have a center of curvature offset from the axis of rotation, and a plurality of peaked shoulders are distributed about the periphery of the plate rearwardly of the tooth support portions. A plurality of hook-shaped gullets are further distributed about the periphery of the plate between the shoulders and the cutting teeth. A fiber cement board is then provided, and the board is cut using the power tool.
The saw blades of the preferred embodiments described herein provide improved means for cutting fiber cement materials such as flat rock wallboards and DUROCK(copyright) fiber board products. DUROCK(copyright) products are cement board products specially manufactured for use in potentially wet environments, such as for backing ceramic tile. The improved design disclosed herein incorporates fewer teeth than conventional blades and produces significantly less dust than conventional blade designs. The improved design also results in blades having a significantly longer life span than prior art blade designs or conventional carbide blades when used with fiber cement materials. The disclosed blades may be utilized with conventional-drive or worm-drive handheld circular saws or table saw equipment, and can facilitate all aspects of construction where fiber cement materials are used.